1. Field of the Invention
The present invention relates to high frequency switching components, and more particularly, the invention relates to high frequency switching components formed by using a multilayer circuit board so as to prevent noise.
2. Related Art
In digital portable phones, high frequency switches are connected to transmission circuits, reception circuits, and antennas to be used for switching connections between the transmission circuits and the antennas, and connections between the reception circuits and the antennas.
For example, Japanese Unexamined Patent Application Publication No. 7-202502 provides a high frequency switching component comprising such a high frequency switch, which is of keen interest to the background of the present invention.
The high frequency switching component is formed by using a multilayer circuit board. Circuit elements forming a high frequency switch are disposed in the multilayer circuit board and on a surface thereof, by which miniaturization of the high frequency switching component is achieved. With this arrangement, an area necessary to mount the high frequency switching component can be reduced.
In a high frequency circuit incorporating such a high frequency switch, it is essential to take measures for reducing noise, including electrostatic surges, that is, surge currents which occur when built-up static electricity is discharged.
In order to prevent such noise, conventionally, a separate noise-preventing component has been mounted on an appropriate wiring board with the high frequency switching component.
However, in such an arrangement, it is necessary to allocate an area for mounting the noise-preventing component on the wiring board. As a result, this arrangement is a hindrance to the miniaturization of the wiring board. In addition, since the noise-preventing component is required to be a discrete component, this causes an increase in cost.
As another conventional noise-preventing measure, a resin coating is applied on an antenna to prevent an electrostatic current surge from entering the antenna.
However, the resin coating can come off due to deterioration of the resin. Under such circumstances, an electrostatic surge can cause great damage to the high-frequency switch, or to an external circuit connected to the antenna or the high-frequency switch, and can lead even to the destruction of the external circuit.
As noise-preventing components, varistors and Zener diodes are known. When a varistor or a Zener diode is used as a component for preventing electrostatic surges, the capacitance between terminals must be increased. Thus, these components cannot be used in a signal line, and accordingly cannot be used for preventing electrostatic surges in a high frequency circuit incorporating such a high frequency switch.